A Study for S-wave Velocity Structure Using Spiral MASW and Pentagon SPAC Arrays

An experimental survey was carried out to compare and combine the active and passive surface wave methods in Granada, South Spain. The active survey data for MASW were collected by linear and spiral arrays. While the result of the linear array analysis is an average over the survey line, the spiral array analysis addresses S-wave velocity of areal coverage. The passive survey data for the SPAC analysis were acquired using six-point arrays of equilateral pentagon and the centre configuration in three sizes. A downhole S-wave survey was also conducted in a borehole in the vicinity.

The S-wave velocity structures estimated from the MASW survey were comparable with the borehole survey data down to about 30 metres below the ground surface. On the other hand the SPAC analysis can estimate S-wave velocity structure far deeper than the borehole and MASW survey could reach: over 200 metres underground. Combining the MASW and SPAC analyses, a comprehensive velocity structure was estimated to a deep basement rocks with a shallow alluvial structure with higher resolution.